Multi-layer mask for substrate dicing by laser and plasma etch

ABSTRACT

Methods of dicing substrates having a plurality of ICs. A method includes forming a multi-layered mask comprising a first mask material layer soluble in a solvent over the semiconductor substrate and a second mask material layer, insoluble in the solvent, over the first mask material layer. The multi-layered mask is patterned with a laser scribing process to provide a patterned mask with gaps. The patterning exposes regions of the substrate between the ICs. The substrate is then plasma etched through the gaps in the patterned mask to singulate the IC with the second mask material layer protecting the first mask material layer for at least a portion of the plasma etch. The soluble material layer is dissolved subsequent to singulation to remove the multi-layered mask.

This is a Continuation application of Ser. No. 13/161,427 filed Jun. 15,2011, which is presently pending and which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention pertain to the field ofsemiconductor processing and, in particular, to masking methods fordicing substrates, each substrate having an integrated circuit (IC)thereon.

BACKGROUND DESCRIPTION OF RELATED ART

In semiconductor substrate processing, ICs are formed on a substrate(also referred to as a wafer), typically composed of silicon or othersemiconductor material. In general, thin film layers of variousmaterials which are either semiconducting, conducting or insulating areutilized to form the ICs. These materials are doped, deposited andetched using various well-known processes to simultaneously form aplurality of ICs, such as memory devices, logic devices, photovoltaicdevices, etc, in parallel on a same substrate.

Following device formation, the substrate is mounted on a supportingmember such as an adhesive film stretched across a film frame and thesubstrate is “diced” to separate each individual device or “die” fromone another for packaging, etc. Currently, the two most popular dicingtechniques are scribing and sawing. For scribing, a diamond tippedscribe is moved across a substrate surface along pre-formed scribelines. Upon the application of pressure, such as with a roller, thesubstrate separates along the scribe lines. For sawing, a diamond tippedsaw cuts the substrate along the streets. For thin substratesingulation, such as <150 μm thick bulk silicon singulation, theconventional approaches have yielded only poor process quality. Some ofthe challenges that may be faced when singulating die from thinsubstrates may include microcrack formation or delamination betweendifferent layers, chipping of inorganic dielectric layers, retention ofstrict kerf width control, or precise ablation depth control.

While plasma dicing has also been contemplated, a standard lithographyoperation for patterning resist may render implementation costprohibitive. Another limitation possibly hampering implementation ofplasma dicing is that plasma processing of commonly encountered metals(e.g., copper) in dicing along streets can create product issues orthroughput limits. Finally, masking of the plasma dicing process may beproblematic, depending on, inter alia, the thickness and top surfacetopography of the substrate, the selectivity of the plasma etch, andremoval of the mask selectively from the materials present on the topsurface of the substrate.

SUMMARY

Embodiments of the present invention include methods of maskingsemiconductor substrates for a hybrid dicing process including bothlaser scribing and plasma etching.

In an embodiment, a method of dicing a semiconductor substrate having aplurality of ICs includes forming a mask over the semiconductorsubstrate, the mask including a plurality of distinct material layerscovering and protecting the ICs. The mask is patterned with a laserscribing process to provide a patterned mask with gaps, exposing regionsof the substrate between the ICs. The substrate is then plasma etchedthrough the gaps in the patterned mask to singulate the ICs into chips.

In another embodiment, a system for dicing a semiconductor substrateincludes a femtosecond laser; a plasma etch chamber, and a maskdeposition module, coupled to a same platform.

In another embodiment, a method of dicing a substrate having a pluralityof ICs includes forming a bi-layer mask including a soluble materiallayer, such as poly (vinyl-alcohol) over a front side of a siliconsubstrate. Over the soluble material layer is a non-soluble materiallayer, such as photoresist or polyimide (PI). The bi-layer mask coversand protects ICs disposed on the front side of the substrate. The ICsinclude a copper bumped top surface having bumps surrounded by apassivation layer, such as polyimide (PI). Subsurface thin films belowthe bumps and passivation include a low-κ interlayer dielectric (ILD)layer and a layer of copper interconnect. The bi-layer mask, thepassivation layer, and subsurface thin films are patterned with afemtosecond laser scribing process to expose regions of the siliconsubstrate between the ICs. The silicon substrate is etched through thegaps with a deep silicon plasma etch process to singulate the ICs andthe bi-layer mask is then wet processed to dissolve the soluble layerand lift off the non-soluble layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not limitation, in the figures of the accompanying drawings inwhich:

FIG. 1 is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation method, in accordance with an embodiment of the presentinvention;

FIG. 2A is a flow diagram illustrating a method of spin coating amulti-layer mask onto a substrate to be diced, in accordance with anembodiment of the present invention;

FIG. 2B is a flow diagram illustrating a method of vapor depositing amulti-layer mask to a substrate to be diced, in accordance with anembodiment of the present invention;

FIG. 3A is a flow diagram illustrating a method of applying amulti-layered mask to a substrate prior to wafer thinning, in accordancewith an embodiment of the present invention;

FIG. 3B is a flow diagram illustrating a method of applying amulti-layered mask to a substrate subsequent to wafer thinning, inaccordance with an embodiment of the present invention;

FIG. 4A illustrates a cross-sectional view of a semiconductor substrateincluding a plurality of ICs corresponding to operations 102A and 102Bof the dicing method illustrated in FIG. 1, in accordance with anembodiment of the present invention;

FIG. 4B illustrates a cross-sectional view of a semiconductor substrateincluding a plurality of ICs corresponding to operation 103 of thedicing method illustrated in FIG. 1, in accordance with an embodiment ofthe present invention;

FIG. 4C illustrates a cross-sectional view of a semiconductor substrateincluding a plurality of ICs corresponding to operation 105 of thedicing method illustrated in FIG. 1, in accordance with an embodiment ofthe present invention;

FIG. 4D illustrates a cross-sectional view of a semiconductor substrateincluding a plurality of ICs corresponding to operation 107 of thedicing method illustrated in FIG. 1, in accordance with an embodiment ofthe present invention;

FIG. 5 illustrates a cross-sectional view of a water soluble maskapplied to over a top surface and subsurface thin films of a substrateincluding a plurality of ICs, in accordance with embodiments of thepresent invention;

FIG. 6 illustrates a block diagram of a tool layout for laser and plasmadicing of substrates with an integrated deposition module for in-situapplication of a multi-layered mask, in accordance with an embodiment ofthe present invention; and

FIG. 7 illustrates a block diagram of an exemplary computer system whichcontrols automated performance of one or more operation in the masking,laser scribing, plasma dicing methods described herein, in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Methods and apparatuses for dicing substrates are described. In thefollowing description, numerous specific details are set forth, such asfemtosecond laser scribing and deep silicon plasma etching conditions inorder to describe exemplary embodiments of the present invention.However, it will be apparent to one skilled in the art that embodimentsof the present invention may be practiced without these specificdetails. In other instances, well-known aspects, such as IC fabrication,substrate thinning, taping, etc., are not described in detail to avoidunnecessarily obscuring embodiments of the present invention. Referencethroughout this specification to “an embodiment” means that a particularfeature, structure, material, or characteristic described in connectionwith the embodiment is included in at least one embodiment of theinvention. Thus, the appearances of the phrase “in an embodiment” invarious places throughout this specification are not necessarilyreferring to the same embodiment of the invention. Furthermore, theparticular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments. Also, it isto be understood that the various exemplary embodiments shown in thefigures are merely illustrative representations and are not necessarilydrawn to scale.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe structural relationships between components.It should be understood that these terms are not intended as synonymsfor each other. Rather, in particular embodiments, “connected” may beused to indicate that two or more elements are in direct physical orelectrical contact with each other. “Coupled” my be used to indicatethat two or more elements are in either direct or indirect (with otherintervening elements between them) physical or electrical contact witheach other, and/or that the two or more elements co-operate or interactwith each other (e.g., as in a cause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one material layer with respect to other materiallayers. As such, for example, one layer disposed over or under anotherlayer may be directly in contact with the other layer or may have one ormore intervening layers. Moreover, one layer disposed between two layersmay be directly in contact with the two layers or may have one or moreintervening layers. In contrast, a first layer “on” a second layer is incontact with that second layer. Additionally, the relative position ofone layer with respect to other layers is provided assuming operationsare performed relative to a substrate without consideration of theabsolute orientation of the substrate.

Generally, a hybrid substrate or substrate dicing process involving aninitial laser scribe and subsequent plasma etch is implemented with amulti-layered mask for die singulation. The laser scribe process may beused to cleanly remove an unpatterned (i.e., blanket) mask including atleast two layers, a passivation layer, and subsurface thin film devicelayers along streets between adjacent ICs. The laser ablation processmay then be terminated upon exposure of, or partial ablation of, thesubstrate. The plasma etch portion of the hybrid dicing process thenetches through the bulk of the substrate, such as through bulk singlecrystalline silicon, for singulation or dicing of chips.

In accordance with an embodiment of the present invention, a combinationof femtosecond laser scribing and plasma etching is used to dice asemiconductor substrate into individualized or singulated ICs. In oneembodiment, femtosecond laser scribing is an essentially, if notcompletely, a non-equilibrium process. For example, thefemtosecond-based laser scribing may be localized with a negligiblethermal damage zone. In an embodiment, laser scribing is used tosingulate ICs having ultra-low κ films (i.e., with a dielectric constantbelow 3.0). In one embodiment, direct writing with laser eliminates alithography patterning operation, allowing the masking material to besomething other than a photo resist as is used in photolithography, anda plasma etch-through the bulk of the substrate. In one embodiment,substantially anisotropic etching is used to complete the dicing processin a plasma etch chamber; the anisotropic etch achieving a highdirectionality into the substrate by depositing an etch polymer onsidewalls of the etched trench.

FIG. 1 is a flow diagram illustrating a hybrid laser ablation-plasmaetch singulation process 100, in accordance with an embodiment of thepresent invention. FIGS. 4A-4D illustrate cross-sectional views of asubstrate 406 including first and second ICs 425, 426 corresponding tothe operations in method 100, in accordance with an embodiment of thepresent invention.

Referring to operation 102A of FIG. 1, and corresponding FIG. 4A, afirst mask material 402A of a multi-layered mask 402 is formed above asubstrate 406. Generally, substrate 406 is composed of any materialsuitable to withstand a fabrication process of the thin film devicelayers formed thereon. For example, in one embodiment, substrate 406 isa group IV-based material such as, but not limited to, monocrystallinesilicon, germanium or silicon/germanium. In another embodiment,substrate 406 is a III-V material such as, e.g., a III-V materialsubstrate used in the fabrication of light emitting diodes (LEDs).During device fabrication, the substrate 406 is typically 600 μm-800 μmthick, but as illustrated in FIG. 4A may have been thinned to 100 μm oreven to 50 μm with the thinned substrate now supported by a carrier,such as a backing tape 410 stretched across a support structure of adicing frame (not illustrated) and adhered to a backside of thesubstrate with a die attach film (DAF) 408.

In embodiments, first and second ICs 425, 426 include memory devices orcomplimentary metal-oxide-semiconductor (CMOS) transistors fabricated ina silicon substrate 406 and encased in a dielectric stack. A pluralityof metal interconnects may be formed above the devices or transistors,and in surrounding dielectric layers, and may be used to electricallycouple the devices or transistors to form the ICs 425, 426. Materialsmaking up the street 427 may be similar to or the same as thosematerials used to form the ICs 425, 426. For example, street 427 mayinclude thin film layers of dielectric materials, semiconductormaterials, and metallization. In one embodiment, the street 427 includesa test device similar to the ICs 425, 426. The width of the street 427may be anywhere between 10 μm and 200 μm, measured at the thin filmdevice layer stack/substrate interface.

In embodiments, the multi-layered mask 402 is a bi-layer with the firstmask material layer 402A formed at operation 102A to be in contact witha top surface of the ICs 425, 426. The multi-layered mask 402 alsocovers the intervening street 427 between the ICs 425, 426. At operation102B, a second mask material layer 402B is disposed on the first maskmaterial layer 402A. In further embodiments, additional mask layers maybe applied. The first mask material layer 402A is to provide a means forremoving the second mask material layer 402B from a top surface of theICs 425, 426 while the second mask material layer 402B is to provideadditional protection to the top surface of the ICs 425, 426 (and to thefirst mask material layer 402A) during the hybrid laser ablation-plasmaetch singulation process 100 (FIG. 1). The multi-layered mask 402 isunpatterned prior to the laser scribing operation 103 with the laserscribe to perform a direct writing of the scribe lines by ablatingportions of the multi-layered mask 402 disposed over the street 427.

FIG. 5 illustrates an expanded cross-sectional view 500 of one exemplaryembodiment including a first mask material layer 402A in contact with atop surface of the IC 426 and the street 427. As shown in FIG. 5, thesubstrate 406 has a top surface 503 upon which thin film device layersare disposed which is opposite a bottom surface 502 which interfaceswith the DAF 408 (FIG. 4A). Generally, the thin film device layermaterials may include, but are not limited to, organic materials (e.g.,polymers), metals, or inorganic dielectrics such as silicon dioxide andsilicon nitride. The exemplary thin film device layers illustrated inFIG. 5 include a silicon dioxide layer 504, a silicon nitride layer 505,copper interconnect layers 508 with low-κ (e.g., less than 3.5) or ultralow-κ (e.g., less than 3.0) interlayer dielectric layers (ILD) 507, suchas carbon doped oxide (CDO), disposed there between. A top surface ofthe IC 426 includes a bump 512, typically copper, surrounded by apassivation layer 511, typically a polyimide (PI) or similar polymer.The bumps 512 and passivation layer 511 therefore make up a top surfaceof the IC with the thin film device layers forming subsurface IC layers.The bump 512 extends from a top surface of the passivation layer 511 bya bump height H_(B) which in the exemplary embodiments ranges between 10μm and 50 μm.

With the first mask material layer 402A covered by a second maskmaterial layer 402B, the first mask material layer 402A may functioneither as a means of undercutting the second mask material layer 402B sothat it may be lifted off from the underlying passivation layer 511,bump 512, or as a barrier protecting the passivation layer 511 and/orbump 512 from the process used to strip the second mask material layer402B. Because the first mask material layer 402A covers the bump 412,the lift off will completely remove the multi-layered mask. The secondmaterial composition and thickness may then be freely designed tosurvive the plasma etch process even over the very tall bump 512 (which,being copper, may be damaged, oxidized, or otherwise contaminated ifexposed to the plasma) without being constrained by the mask stripping.

Referring to FIG. 5, in the street, the maximum thickness T_(max) of themulti-layered mask 402 in the street 427 is generally limited by theability of a laser to pattern through the mask by ablation. Themulti-layered mask 402 may be much thicker over the ICs 425, 426 and oredges of the street 427 where no street pattern is to be formed. Assuch, T_(max) is a function of laser power and the optical conversionefficiency associated with laser wavelength. As T_(max) is associatedwith the street 427, street feature topography, street width, and themethod of applying the multi-layered mask 402 may be designed to limitT_(max) to a thickness which can be ablated along with underlying thinfilm device layers in one or more laser passes, depending on throughputrequirements. In particular embodiments, the multi-layered mask 402 hasa street mask thickness T_(max) which is less than 30 μm andadvantageously less than 20 μm with a thicker mask calling for multiplelaser passes. In particular embodiments, the first mask material layer402A is thinner than the second mask material layer 402B. For exemplaryembodiments, the first mask material layer 402A is not more than halfthe thickness of the second mask material layer 402B (e.g., the firstmask material layer 402A accounts for no more than half of the streetmask thickness T_(max)).

As further shown in FIG. 5, the minimum thickness T_(min) of themulti-layered mask 402, found on a top surface of the bump 512 (being ofmost extreme topography), is a function of the selectivity achieved bythe subsequent plasma etch (e.g., operation 105 in FIG. 1) over thesecond mask material layer 402B. The plasma etch selectivity isdependent on at least both the material/composition of the second maskmaterial layer 402B and the etch process employed.

As oxidative plasma cleans, acidic etchants, and many other conventionalmask stripping processes may not be compatible with the bump 512 and/orpassivation layer 511, in an embodiment, the first mask material layer402A is a polymer soluble in a solvent which is selective to, theunderlying passivation layer 511 and/or bump 512. In a furtherembodiment, the first mask material layer 402A is also thermally stableto at least 60° C., preferably stable at 100° C., and ideally stable to120° C. to avoid excessive crosslinking during the subsequent formationof the second mask layer or plasma etch process when the material'stemperature will be elevated (e.g., through application of plasma power.Generally, excessive crosslinking adversely affects the solubility ofthe material, making removal of the multi-layered mask 402 moredifficult.

In one embodiment, the first mask material layer 402A is of a materialsoluble in water. In one such embodiment, the water soluble materialcomprises a water soluble polymer. Selection of water soluble materialfor the present invention is complicated by thermal stabilityrequirements, mechanics of applying/removing the material to/from thesubstrate, and IC contamination concerns. Exemplary water solublematerials having sufficient thermal stability include any of: poly(vinylalcohol), poly(acrylic acid), poly(methacrylic acid), poly(acrylamide),poly(ethylene oxide), or the like. For the exemplary embodimentemploying PVA, thermal stability has been confirmed for 60° C. withsolubility decreasing as the temperature approaches 150° C. As such, fora PVA embodiment, processing after operation 102A until themulti-layered mask 402 is removed (i.e., plasma etching of the street427) advantageously maintains the first mask layer 402A at a temperaturebelow 150° C., preferably below 100° C., and ideally below 80° C.

In another embodiment, the first mask material layer 402A is soluble inany commercially available aqueous or hydrocarbon wet cleaning agentcompatible with the materials employed for the passivation layer 511 andbump 512. Exemplary mask materials include non-photosensitive organicpolymeric materials, such as any of those listed above where sufficientcrosslinking has occurred to require a solvent such as isopropyl alcohol(IPA), tramethylammonium hydroxide (TMAH), etc.

Depending on the embodiment, the first mask material layer 402A is wetapplied onto the substrate 406 to cover the passivation layer 511 andbump 512, vapor deposited, or applied as a dry film laminate. In a firstembodiment, the first mask material layer 402A is merely sprayed ontothe substrate. In a further embodiment, the first mask material layer402A spin coated onto the substrate.

FIG. 2A is a flow diagram illustrating a masking method 200 for spincoating the first mask material layer 402A onto a substrate to be diced,in accordance with an embodiment of the present invention. At operation202, a substrate is loaded onto a spin coat system or transferred into aspin coat module of an integrated platform. At operation 204 a polymericprecursor solution is spun over the passivation layer 511 and bump 512.For the exemplary water soluble first mask material layer, the polymericprecursor solution is an aqueous solution. Experiments conducted withspin-on PVA solutions have demonstrated coverage of bumps with a height(H_(B)) of 50 μm.

At operation 208 the wet coat is dried or baked, for example on a hotplate, and the substrate unloaded for laser scribe or transferredin-vaccuo to a laser scribe module. For particular embodiments where thefirst mask material layer 402A is hygroscopic, in-vaccuo transfer isadvantageous. The spin and dispense parameters are a matter of choicedepending on the material, substrate topography and desired first maskmaterial layer thickness. The bake temperature and time should beselected to avoid excessive crosslinking which renders removaldifficult. Exemplary drying temperatures ranging from 60° C. to 150° C.,depending on the material.

In the exemplary embodiment where the first mask material layer 402A isspin-coated (as illustrated in FIG. 2A), the second mask material layer402B is also spin-coated (at operation 210). For such embodiments, thesecond mask material layer 402B may be any conventional polymericmaterial offering suitable resistance to plasma etch, such as, but notlimited to, any known photoresist, polyimide (PI), Benzo-Cyclo-Butene(BCB), or the like. The spin and dispense parameters are again a matterof choice depending on the material, substrate topography and desiredthickness of the second mask material layer 402B (as a function of etchresistance, etc.). At operation 212, the second mask material layer 402Bis dried with a bake temperature and bake time which will avoidexcessive crosslinking of the first mask material layer 402A. Exemplarydrying temperatures ranging from 60° C. to 150° C., depending on thematerial. Operation 220 then completes the masking method 200 with thesubstrate unloaded for subsequent scribing or transferred in-vaccuo to alaser scribe apparatus of an integrated platform.

In another embodiment, at least one of the first and second maskmaterial layer 402A, 402B are formed by vapor deposition. FIG. 2B is aflow diagram illustrating an exemplary masking method 2B for applyingthe second mask material layer 402B, in accordance with an embodiment ofthe present invention. At operation 205, the first mask material layer402A is formed by any manner described elsewhere herein (e.g., spincoat, spray, vapor deposit, dry laminate). At operation 211, the secondmask material layer 402B is formed over the first mask material layer402A by chemical vapor deposition. In the exemplary embodiment, a lowtemperature chemical vapor deposition process is employed to form a CVDcarbon layer. Because the CVD carbon layer may contain a plurality ofbonding states in various proportions, it lacks long rang order and sois commonly referred to as “amorphous carbon.” An amorphous carbonmaterial is commercially available from Applied Materials, Inc., CA,U.S.A. under the trade name Advanced Patterning Film™ (APF). In certainembodiments, the amorphous carbon layer is formed with a PECVD processusing hydrocarbon precursors, such as, but not limited to, methane(CH₄), propylene (C₃H₆), propyne (C₃H₄), propane (C₃H₈), butane (C₄H₁₀),butylenes (C₄H₈), butadiene (C₄H₆), acetelyne (C₂H₂) and mixturesthereof. The CVD carbon material may also include nitrogen or otheradditives. A low-temperature CVD process is preferable where there is arisk of cross-linking the first mask material layer 402A. For exampleduring deposition of the CVD carbon layer, wafer temperature may bemaintained under 150° C., or even under 100° C. if necessary, dependingon the first mask material. With moderate plasma ion density, littlesubstrate heating is necessary for a CVD film of sufficient quality toaugment the first mask material layer 402A and provide etch resistanceof between 1:20 and 1:30 during the subsequent plasma street etch. Inthe exemplary embodiment where the first mask material 402A is watersoluble (e.g., PVA), the second mask material 402B is amorphous carbondeposited with a carbonaceous precursor gas at a temperature below 100°C. Operation 220 then completes the masking method 200 with thesubstrate unloaded for subsequent scribing or transferred in-vaccuo to alaser scribe apparatus of an integrated platform.

Depending on the embodiment, either of the masking method 200 or maskingmethod 250 may be performed prior to, or subsequent to, a backside grind(BSG) process. As spin coating is generally an accomplished techniquefor substrates having a conventional thickness of 750 μm, the maskingmethod 200 may be advantageously performed prior to backside grind.However, in the alternative, the masking method 200 is performedsubsequent to the backside grind, for example by supporting both athinned substrate and taped frame upon a rotatable chuck.

FIG. 3A is a flow diagram illustrating a method 300 for applying themulti-layered mask 402 to a substrate to be diced prior to waferthinning. Method 300 begins with receiving a bumped and passivatedsubstrate at operation 355. At operation 304, at least the first maskmaterial layer 402A is formed. In a further embodiment, both the firstmask material layer 402A and second mask material layer 402B are formed.Operation 304 may therefore entail any of the formation methodsdescribed for the first mask material layer and/or the second maskmaterial layer, as described elsewhere herein. At operation 360,frontside tape is applied over at least the first layer of themulti-layered mask 402. Any conventional frontside tape, such as, butnot limited to UV-tape, may be applied over the first layer of themulti-layered mask 402. At operation 370, the substrate is thinned fromthe backside, for example by grinding the bottom surface 502 of thesubstrate 406 (FIG. 5). At operation 375, a backside support 411 isadded to the thinned substrate. For example, the backside tape 410 maybe applied and the frontside tape then removed from the substrate withat least the first layer of the multi-layered mask 402 remaining. Method300 then returns to operation 103 (FIG. 1) to complete the multi-layeredmasking process or proceed with the hybrid laser ablation-plasma etchsingulation method 300, in accordance with embodiments of the presentinvention.

FIG. 3B is a flow diagram illustrating a method 350 for applying themulti-layered mask 402 to a substrate to be diced subsequent to waferthinning. Method 350 begins with receiving a bumped and passivatedsubstrate at operation 355. At the operation 360, any conventionalfrontside tape, such as, but not limited to UV-tape is applied over theICs. At operation 370, the substrate is thinned from the backside, forexample by grinding the bottom surface 502 of the substrate 406illustrated in FIG. 5. At operation 375, a backside support 411 is addedto the thinned substrate. For example, the backside tape 410 may beapplied and the frontside tape then removed from the water soluble masklayer. At operation 304, at least the second mask material layer 402B isthen formed (e.g., by spin coat, CVD, dry film lamination, etc.). In afurther embodiment, both the first mask material layer 402A and secondmask material layer 402B are formed. Operation 304 may again entail anyof the formation methods described for the second mask material layerand/or the first mask material layer, as described elsewhere herein.Method 350 then returns to FIG. 1 to proceed with the hybrid laserablation-plasma etch singulation method 300.

In a further embodiment, the methods 300 and 350 are both practiced withthe first mask material layer 402A being formed prior to BSG (asillustrated by FIG. 3A) and the second mask material layer 402B beingformed subsequent to BSG (as illustrated by FIG. 3A). In one suchembodiment the first mask material layer 402A is applied with thespin-coat technique while the substrate is full thickness and the secondmask material layer 402B is applied to a thinned substrate with anon-spin-coat technique, such as vapor deposition. For example,referring to FIG. 3A, a PVA first mask material layer 402A may beapplied at operation 304 prior to the frontside taping at operation 360while a CVD carbon second mask material layer 402B may be applied atoperation 304 subsequent to frontside detaping operation 375.

Returning now to operation 103 of method 100, and corresponding FIG. 4B,the multi-layered mask 402 is patterned by ablation with a laserscribing process forming trenches 412, extending the subsurface thinfilm device layers, and exposing regions of the substrate 406 betweenthe ICs 425, 426. As such, the laser scribing process is used to ablatethe thin film material of the streets 427 originally formed between theICs 425, 426. In accordance with an embodiment of the present invention,patterning the multi-layered mask 402 with the laser-based scribingprocess includes forming trenches 414 partially into the regions of thesubstrate 406 between the ICs 425, 426, as depicted in FIG. 4B.

In the exemplary embodiment illustrated in FIG. 5, the laser scribingdepth D_(L) is approximately in the range of 5 μms to 50 μms deep,advantageously in the range of 10 μms to 20 μms deep, depending on thethickness T_(F) of the passivation 511 and subsurface thin film devicelayers and thickness T_(max) of the multi-layered mask 402.

In an embodiment, the multi-layered mask 402 is patterned with a laserhaving a pulse width (duration) in the femtosecond range (i.e., 10⁻¹⁵seconds), referred to herein as a femtosecond laser. Laser parametersselection, such as pulse width, may be critical to developing asuccessful laser scribing and dicing process that minimizes chipping,microcracks and delamination in order to achieve clean laser scribecuts. A laser frequency in the femtosecond range advantageouslymitigates heat damage issues relative longer pulse widths (e.g.,picosecond or nanosecond). Although not bound by theory, as currentlyunderstood a femtosecond energy source avoids low energy recouplingmechanisms present for picosecond sources and provides for greaterthermal nonequilibrium than does a nanosecond-source. With nanosecond orpicoseconds laser sources, the various thin film device layer materialspresent in the street 427 behave quite differently in terms of opticalabsorption and ablation mechanisms. For example, dielectrics layers suchas silicon dioxide, is essentially transparent to all commerciallyavailable laser wavelengths under normal conditions. By contrast,metals, organics (e.g., low-κ materials) and silicon can couple photonsvery easily, particularly nanosecond-based or picosecond-based laserirradiation. If non-optimal laser parameters are selected, in a stackedstructures that involve two or more of an inorganic dielectric, anorganic dielectric, a semiconductor, or a metal, laser irradiation ofthe street 427 may disadvantageously cause delamination. For example, alaser penetrating through high bandgap energy dielectrics (such assilicon dioxide with an approximately of 9 eV bandgap) withoutmeasurable absorption may be absorbed in an underlying metal or siliconlayer, causing significant vaporization of the metal or silicon layers.The vaporization may generate high pressures potentially causing severeinterlayer delamination and microcracking. Femtosecond-based laserirradiation processes have been demonstrated to avoid or mitigate suchmicrocracking or delamination of such material stacks.

Parameters for a femtosecond laser-based process may be selected to havesubstantially the same ablation characteristics for the inorganic andorganic dielectrics, metals, and semiconductors. For example, theabsorptivity/absorptance of silicon dioxide is non-linear and may bebrought more in-line with that of organic dielectrics, semiconductorsand metals. In one embodiment, a high intensity and short pulse widthfemtosecond-based laser process is used to ablate a stack of thin filmlayers including a silicon dioxide layer and one or more of an organicdielectric, a semiconductor, or a metal. In accordance with anembodiment of the present invention, suitable femtosecond-based laserprocesses are characterized by a high peak intensity (irradiance) thatusually leads to nonlinear interactions in various materials. In onesuch embodiment, the femtosecond laser sources have a pulse widthapproximately in the range of 10 femtoseconds to 450 femtoseconds,although preferably in the range of 50 femtoseconds to 400 femtoseconds.

In certain embodiments, the laser emission spans any combination of thevisible spectrum, the ultra-violet (UV), and/or infra-red (IR) spectrumsfor a broad or narrow band optical emission spectrum. Even forfemtosecond laser ablation, certain wavelengths may provide betterperformance than others. For example, in one embodiment, afemtosecond-based laser process having a wavelength closer to or in theUV range provides a cleaner ablation process than a femtosecond-basedlaser process having a wavelength closer to or in the IR range. In aspecific embodiment, a femtosecond laser suitable for semiconductorsubstrate or substrate scribing is based on a laser having a wavelengthof approximately less than or equal to 540 nanometers, althoughpreferably in the range of 540 nanometers to 250 nanometers. In aparticular embodiment, pulse widths are less than or equal to 400femtoseconds for a laser having a wavelength less than or equal to 540nanometers. However, in an alternative embodiment, dual laserwavelengths (e.g., a combination of an IR laser and a UV laser) areused.

In one embodiment, the laser and associated optical pathway provide afocal spot at the work surface approximately in the range of 3 μm to 15μm, though advantageously in the range of 5 μm to 10 μm. The spatialbeam profile at the work surface may be a single mode (Gaussian) or havea beam shaped top-hat profile. In an embodiment, the laser source has apulse repetition rate approximately in the range of 300 kHz to 10 MHz,although preferably approximately in the range of 500 kHz to 5 MHz. Inan embodiment, the laser source delivers pulse energy at the worksurface approximately in the range of 0.5 μJ to 100 μJ, althoughpreferably approximately in the range of 1 μJ to 5 μJ. In an embodiment,the laser scribing process runs along a work piece surface at a speedapproximately in the range of 500 mm/sec to 5 m/sec, although preferablyapproximately in the range of 600 mm/sec to 2 m/sec.

The scribing process may be run in single pass only, or in multiplepasses, but is advantageously no more than two passes. The laser may beapplied either in a train of single pulses at a given pulse repetitionrate or a train of pulse bursts. In an embodiment, the kerf width of thelaser beam generated is approximately in the range of 2 μms to 15 μm,although in silicon substrate scribing/dicing preferably approximatelyin the range of 6 μm to 10 μm, as measured at a device/siliconinterface.

Returning to FIGS. 1 and 4C, the substrate 406 is etched through thetrenches 412 in the patterned multi-layered mask 402 to singulate theICs 425, 426. In accordance with an embodiment of the present invention,etching the substrate 406 includes etching the trenches 412 formed withthe femtosecond-based laser scribing process to ultimately etch entirelythrough substrate 406, as depicted in FIG. 4C.

In an embodiment, etching the substrate 406 includes using ananisotropic plasma etching process 416. In one embodiment, a throughsubstrate etch process is used with the second mask material layer 402Bprotecting the first mask material layer 402A from plasma exposure forthe entire duration of plasma etch. In an alternative embodiment, thesecond mask material layer 402B is consumed during the plasma etch tothe point that the first mask layer 402A is exposed to the plasma priorto completion of the etch. A high-density plasma source operating athigh powers may be used for the plasma etching operation 105. Exemplarypowers range between 3 kW and 6 kW, or more to achieve an etch rate ofthe substrate 406 that is greater than 25 μms per minute.

In an exemplary embodiment, a deep anisotropic silicon etch (e.g., athrough silicon via etch) is used to etch a single crystalline siliconsubstrate or substrate 406 at an etch rate greater than approximately40% of conventional silicon etch rates while maintaining essentiallyprecise profile control and virtually scallop-free sidewalls. Effects ofthe high power on the multi-layered mask (particularly the first maskmaterial layer 402A) are controlled through application of cooling powervia an electrostatic chuck (ESC) chilled to −10° C. to −15° C. tomaintain the first mask material layer 402A at a temperature below 100°C. and preferably between 70° C. and 80° C. throughout the duration ofthe plasma etch process. At such temperatures, solubility of the firstmask material layer 402A may be advantageously maintained.

In a specific embodiment, the plasma etch entails a plurality ofprotective polymer deposition cycles interleaved over time with aplurality of etch cycles. The deposition:etch duty cycle may vary withthe exemplary duty cycle being approximately 1:1. For example, the etchprocess may have a deposition cycle with a duration of 250 ms-750 ms andan etch cycle of 250 ms-750 ms. Between the deposition and etch cycles,an etching process chemistry, employing for example SF₆ for theexemplary silicon etch embodiment, is alternated with a depositionprocess chemistry, employing a polymerizing C_(x)F_(y) gas such as, butnot limited to, C₄F₆ or C₄F₈. Process pressures may further bealternated between etch and deposition cycles to favor each in theparticular cycle, as known in the art.

The hybrid laser ablation-plasma etch singulation method 300 is thencompleted at operation 107 with removal of the mask layer 402. In theexemplary embodiment illustrated in FIG. 4D, the mask removal operation107 entails dissolving the first mask material layer 402A selectively tothe ICs 425, 426 (e.g., selectively to passivation layer 511, bump 512)as well as selectively to the second mask material layer 402B. Thesecond mask material layer 402B is thereby lifted-off. In one embodimentwhere the first mask material layer 402A is water soluble, the watersoluble mask layer is washed off with a pressurized jet of de-ionizedwater or through submergence of the substrate in an ambient or heatedwater bath. In alternative embodiments, the multi-layered mask 402 maybe lifted off with aqueous or hydrocarbon solvent solutions known in theart to dissolve the particular material utilized for the first maskmaterial layer 402A. As further illustrated in FIG. 4D, either of thesingulation process or mask removal process may further includepatterning the die attach film 908, exposing the top portion of thebacking tape 910.

A single integrated platform 600 may be configured to perform many orall of the operations in the hybrid laser ablation-plasma etchsingulation process 100. For example, FIG. 6 illustrates a block diagramof a cluster tool 606 coupled with laser scribe apparatus 610 for laserand plasma dicing of substrates, in accordance with an embodiment of thepresent invention. Referring to FIG. 6, the cluster tool 606 is coupledto a factory interface 602 (FI) having a plurality of load locks 604.The factory interface 602 may be a suitable atmospheric port tointerface between an outside manufacturing facility with laser scribeapparatus 610 and cluster tool 606. The factory interface 602 mayinclude robots with arms or blades for transferring substrates (orcarriers thereof) from storage units (such as front opening unifiedpods) into either cluster tool 606 or laser scribe apparatus 610, orboth.

A laser scribe apparatus 610 is also coupled to the FI 602. In anembodiment, the laser scribe apparatus 610 includes a femtosecond laser.The femtosecond laser to performing the laser ablation portion of thehybrid laser and etch singulation process 100. In one embodiment, amoveable stage is also included in laser scribe apparatus 610, themoveable stage configured for moving a substrate or substrate (or acarrier thereof) relative to the femtosecond-based laser. In a specificembodiment, the femtosecond laser is also moveable.

The cluster tool 606 includes one or more plasma etch chambers 608coupled to the FI by a robotic transfer chamber 650 housing a roboticarm for in-vaccuo transfer of substrates. The plasma etch chambers 608is suitable for performing a plasma etch portion of the hybrid laser andetch singulation process 100. In one exemplary embodiment, the plasmaetch chamber 608 is further coupled to an SF₆ gas source and at leastone of a C₄F₈ and C₄F₆ source. In a specific embodiment, the one or moreplasma etch chambers 608 is an Applied Centura® Silvi^(a)™ Etch system,available from Applied Materials of Sunnyvale, Calif., USA, althoughother suitable etch systems are also available commercially. In anembodiment, more than one etch chamber 608 is included in the clustertool 606 portion of integrated platform 600 to enable high manufacturingthroughput of the singulation or dicing process.

The cluster tool 606 may include other chambers suitable for performingfunctions in the hybrid laser ablation-plasma etch singulation process100. In the exemplary embodiment illustrated in FIG. 6, the cluster tool606 includes both a mask formation module 612 and a solvent wet station614, though either may be provided in absence of the other. Depending onthe embodiment, the mask formation module 612 may be a spin coatingmodule or a chemical vapor deposition (CVD) chamber. As a spin coatingmodule, a rotatable chuck is configured to clamp by vacuum, orotherwise, a thinned substrate mounted on a carrier such as backing tapemounted on a frame. In further embodiments, the spin coating module isfluidly coupled to an aqueous solution source. For CVD chamberembodiments, the mask formation module 612 is configured to deposit aCVD carbon layer. Any commercially available CVD chamber configured forlow temperature film depositions may be coupled to a carbon source gas.

Embodiments of the wet station 614 are to dissolve at least the firstmask material layer (e.g., 402A) after plasma etching the substrate. Thewet station 614 may include for example a pressurized spray jet todispense water other solvent.

FIG. 7 illustrates a computer system 700 within which a set ofinstructions, for causing the machine to execute one or more of thescribing methods discussed herein may be executed, for example toanalyze a reflected light from a tag to identify at least onemicromachine artifact. The exemplary computer system 700 includes aprocessor 702, a main memory 704 (e.g., read-only memory (ROM), flashmemory, dynamic random access memory (DRAM) such as synchronous DRAM(SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 706 (e.g., flashmemory, static random access memory (SRAM), etc.), and a secondarymemory 718 (e.g., a data storage device), which communicate with eachother via a bus 730.

Processor 702 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processor 702 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,etc. Processor 702 may also be one or more special-purpose processingdevices such as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. Processor 702 is configured to executethe processing logic 726 for performing the operations and stepsdiscussed herein.

The computer system 700 may further include a network interface device708. The computer system 700 also may include a video display unit 710(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), analphanumeric input device 712 (e.g., a keyboard), a cursor controldevice 714 (e.g., a mouse), and a signal generation device 716 (e.g., aspeaker).

The secondary memory 718 may include a machine-accessible storage medium(or more specifically a computer-readable storage medium) 731 on whichis stored one or more sets of instructions (e.g., software 722)embodying any one or more of the methodologies or functions describedherein. The software 722 may also reside, completely or at leastpartially, within the main memory 704 and/or within the processor 702during execution thereof by the computer system 700, the main memory 704and the processor 702 also constituting machine-readable storage media.The software 722 may further be transmitted or received over a network720 via the network interface device 708.

The machine-accessible storage medium 731 may also be used to storepattern recognition algorithms, artifact shape data, artifact positionaldata, or particle sparkle data. While the machine-accessible storagemedium 731 is shown in an exemplary embodiment to be a single medium,the term “machine-readable storage medium” should be taken to include asingle medium or multiple media (e.g., a centralized or distributeddatabase, and/or associated caches and servers) that store the one ormore sets of instructions. The term “machine-readable storage medium”shall also be taken to include any medium that is capable of storing orencoding a set of instructions for execution by the machine and thatcause the machine to perform any one or more of the methodologies of thepresent invention. The term “machine-readable storage medium” shallaccordingly be taken to include, but not be limited to, solid-statememories, and optical and magnetic media.

Thus, methods of dicing semiconductor substrates, each substrate havinga plurality of ICs, have been disclosed. The above description ofillustrative embodiments of the invention, including what is describedin the Abstract, is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. While specific implementationsof, and examples for, the invention are described herein forillustrative purposes, various equivalent modifications are possiblewithin the scope of the invention, as those skilled in the relevant artwill recognize. The scope of the invention is therefore to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

What is claimed is:
 1. A method of dicing a substrate comprising a plurality of ICs, the method comprising: forming a multi-layer mask over the substrate covering and protecting the ICs, the multi-layer mask including a first mask material layer disposed on a top surface of the ICs and a second mask material layer disposed over the first mask material layer; patterning the multi-layer mask with a laser scribing process to provide a patterned mask with gaps, exposing regions of the substrate between the ICs; plasma etching the substrate through the gaps in the patterned mask to singulate the ICs, wherein the second mask material layer protects the first mask material layer from exposure to the plasma for at least a portion of etching process; removing at least a portion of the second mask material layer; and subsequent to removing the portion of the second mask material layer, removing the first mask material layer.
 2. The method of claim 1, wherein removing at least the portion of the second mask material layer comprises removing the entire second mask material layer prior to removing the first mask material layer.
 3. The method of claim 1, wherein removing at least the portion of the second mask material layer comprises plasma etching the second mask material layer.
 4. The method of claim 3, wherein plasma etching the second mask material layer comprises using SF₆ and at least one of C₄F₈ and C₄F₆.
 5. The method of claim 1, wherein removing the first mask material layer comprises dissolving the first mask material layer.
 6. The method of claim 5, wherein dissolving the first mask material layer comprises dissolving in an aqueous solution.
 7. The method of claim 1, wherein removing at least the portion of the second mask material layer comprises plasma etching the second mask material layer, and wherein removing the first mask material layer comprises dissolving the first mask material layer.
 8. The method of claim 1, wherein the first mask material layer comprises a water soluble polymer, and wherein etching the semiconductor substrate comprises etching the trenches with a deep trench etch process during which the first mask material layer is maintained below 100° C.
 9. The method of claim 8, wherein the forming the multi-layer mask comprises applying at least one of: poly(vinyl alcohol), poly(acrylic acid), poly(methacrylic acid), poly(acrylamide), or poly(ethylene oxide) as the first mask material layer in contact with the top surface of the IC.
 10. The method of claim 1, wherein forming the multi-layer mask comprises applying a non-water soluble polymer over the first mask material layer.
 11. The method of claim 10, wherein applying the non-water soluble polymer further comprises applying at least one of photoresist and polyimide.
 12. The method of claim 1, wherein forming the multi-layer mask further comprises forming the multi-layered mask to a thickness of no more than 20 μm over the street between the ICs and at least 10 μm over a top bump surface of an IC.
 13. The method of claim 1, wherein patterning the mask further comprises direct writing the pattern with a femtosecond laser having a wavelength less than or equal to 540 nanometers and a laser pulse width less than or equal to 400 femtoseconds.
 14. The method of claim 1, wherein forming the multi-layered mask comprises: spin coating a solution of the first mask material layer onto the top surface of the IC; and spin coating a solution of the second mask material layer, or vapor depositing the second mask material layer, over the first mask material layer.
 15. The method of claim 14, further comprising thinning the substrate with a backside grind process, wherein the spin coating of the first mask material layer is performed after the backside grind.
 16. The method of claim 14, wherein spin coating the solution of the second mask material layer or vapor depositing the second mask material layer over the first mask material layer further comprises chemical vapor depositing an amorphous carbon layer over the first mask material layer.
 17. A method of dicing a semiconductor substrate comprising a plurality of ICs, the method comprising: forming a water soluble mask material layer over a silicon substrate, the water soluble mask material layer covering the ICs disposed on the silicon substrate, the ICs comprising a thin film stack including a layer of silicon dioxide, a layer of low-κ material and a layer of copper; forming a non-water soluble mask material layer over the water soluble mask material layer; patterning the photo-resist layer, the layer of low-κ material, and the layer of copper with a femtosecond laser to expose regions of the silicon substrate between the ICs; and etching the silicon substrate through the gaps to singulate the ICs, the non-water soluble mask material layer protecting the water soluble mask material layer from exposure to plasma through at least a portion of the silicon substrate etching; removing at least a portion of the non-water soluble mask material layer; and subsequent to removing the portion of the non-water soluble mask material layer, removing the water soluble mask material layer.
 18. The method of claim 17, wherein removing at least the portion of the non-water soluble mask material layer comprises removing the entire non-water soluble mask material layer prior to removing the water soluble mask material layer.
 19. The method of claim 17, wherein removing at least the portion of the non-water soluble mask material layer comprises plasma etching the non-water soluble mask material layer, and wherein removing the water soluble mask material layer comprises dissolving the water soluble mask material layer.
 20. The method of claim 17, wherein patterning the layer of silicon dioxide, the layer of low-κ material, and the layer of copper with the femtosecond laser comprises ablating the layer of silicon dioxide prior to ablating the layer of low-κ material and the layer of copper, and wherein etching the silicon substrate comprises exposing the substrate to a plasma of SF₆ and at least one of C₄F₈ and C₄F₆ while maintaining the water soluble mask material layer at a temperature below 100° C.
 21. A system for dicing a substrate comprising a plurality of ICs, the system comprising: a laser scribe module to pattern a multi-layered mask and expose regions of a substrate between the ICs; a plasma etch module physically coupled to the laser scribe module to singulate the ICs by plasma etching of the substrate; a robotic transfer chamber to transfer a laser scribed substrate from the laser scribe module to the plasma etch module, and at least one of a mask formation module or a solvent wet clean module, the mask formation module comprising either a spin coater or a chemical vapor deposition (CVD) chamber.
 22. The system of claim 21, wherein the laser scribe comprises a femtosecond laser having a wavelength less than or equal to 540 nanometers and a pulse width of less than or equal to 400 femtoseconds.
 23. The system of claim 21, comprising the mask formation module, wherein the chemical vapor deposition (CVD) chamber is to deposit a CVD carbon layer.
 24. The system of claim 21, wherein the plasma etch chamber is coupled to SF₆ and at least one of C₄F₈ and C₄F₆. 